1. Field of the Invention
The present invention generally relates to an apparatus for measuring roundness of a work. More particularly, it relates to an apparatus for measuring roundness and method of centering and leveling, which has improved precision and operability in compensation of an eccentricity (centering) and tilt (leveling) of the work.
2. Description of the Related Art
A roundness measuring apparatus is employed to measure a roundness of a cylindrical or tubular work. The work is mounted on a table to trace a circumferential surface (an inner or outer surface) of the work by a detector while the table or the detector itself is rotated around the work. The detector has a mechanical measurement range (stroke) of about 1 mm in common, and an electrical measurement range that decreases as a sensitivity (magnification) is increased. This depends mainly on a constraint from a performance of an AID converter (bit width). If the center of the work is deviated from the rotational center of the table or of the detector at the time of measurement, the detector is required to have a much larger stroke (at least double the eccentricity). This leads the detector to an immeasurable situation in over-stroke, otherwise the sensitivity can not be increased due to the above-mentioned reason. Accordingly, a precise centering is required essentially to perform a high sensitive measurement. Further, when the roundness is measured at a plurality of locations along the height of the work, a tilt of the axial center of the work also causes an eccentricity similar to the above and thus it requires leveling as well.
From the above reasons, the table for receiving the work mounted thereon is provided with mechanisms for centering and leveling (Japanese Patent Nos. 2,569,390 and 2,628,122, for example). The centering mechanism comprises mechanisms for moving the table in X- and Y-axes both perpendicular to the axial center of the work (the vertical axis=Z-axis). These centering axes are hereinafter referred to as CX- and CY-axes. The leveling mechanism comprises mechanisms for positioning the table on a spherical base and pushing the table in X- and Y-axes to slide it along the spherical base. These leveling axes are hereinafter referred to as LX- and LY-axes.
On centering and leveling, the work is first mounted on the table and the detector traces the circumference of the work to position the work at a location inside the stroke of the detector. A height of the detector at this situation is referred to as ZA. A measurement is performed in this situation to collect data, from which a set of central coordinates of the work at the height ZA is derived. Next, the detector is positioned at a height of ZB and another measurement is performed similarly to collect data, from which another set of central coordinates of the work at the height ZB is derived. From these sets of central coordinates of the work at the heights ZA and ZB, an amount of centering (an amount of eccentric compensation) and an amount of leveling (an amount of tilt compensation) of the work in the X- and Y-axes are computed and displayed. The centering and leveling mechanisms comprise micrometer heads. Therefore, these mechanisms can be manipulated manually, on the basis of the amounts of compensation thus displayed, to perform centering and leveling while reading displays on the micrometer heads.
The present invention has an object to provide an apparatus for measuring roundness, which can afford much simplified workability and improved precision to centering and leveling.
The present invention has another object to provide an apparatus for measuring roundness and method of centering and leveling, which can perform precise centering and leveling, thereby reducing a period of time required for setup activities.
The present invention is provided with an apparatus for measuring roundness, which comprises: a table for receiving a work mounted thereon, the work having a circumferential surface with a roundness to be measured; displacement detecting means for detecting displacements on the circumferential surface of the work; rotational driving means for rotationally driving either the table or the displacement detecting means such that the displacement detecting means detects the displacements along the circumferential surface of the work; eccentricity adjusting means for adjusting an eccentricity in the work, the eccentricity adjusting means including an eccentricity adjusting motor to move the table in a plane perpendicular to the rotational axis of the rotational driving means; tilt adjusting means for adjusting a tilt of the work to the rotational axis, the tilt adjusting means including a tilt adjusting motor to incline the table; computing means for calculating the eccentricity and tilt of the work from the displacements on the circumferential surface of the work detected by the displacement detecting means; and eccentricity/tilt compensating means for driving the eccentricity adjusting motor and tilt adjusting motor on the basis of the eccentricity and tilt obtained by the computing means to compensate the eccentricity and tilt.
According to the present invention, the eccentricity adjusting motor and tilt adjusting motor are respectively provided in the means for adjusting the eccentricity in the work and means for adjusting the tilt of the work. In addition, the eccentricity/tilt compensating means drives these motors on the basis of the eccentricity and tilt of the work obtained by the computing means to compensate the eccentricity and tilt of the work. This prevents any sophisticated manual operations and matching errors on manual operations from occurring and can improve the operability and matching precision effectively.
The motors may be controlled in open-loop though, preferably, the apparatus may further comprise detecting means for detecting amounts of movements of the table in a plane perpendicular to the rotational axis and in a tilt direction about the rotational axis. In this case, the eccentricity/tilt compensating means drives the eccentricity adjusting motor and tilt adjusting motor using the amounts of movements of the table detected by the detecting means as amounts of feedback. This enables precise operations of centering and leveling to be performed by feedback control.
When the eccentricity and tilt of the work are obtained by the computing means, the following may be effective, for example. Namely, the computing means calculates central coordinates of the work mounted on the table at a plurality of locations along the rotational axis from the displacements on the locations of the circumferential surface of the work, which are measured by the displacement detecting means. Then, it computes the eccentricity and tilt based on the central coordinates.
The eccentricity/tilt compensating means may drive the eccentricity adjusting motor and tilt adjusting motor simultaneously to further reduce a period of compensation time.
The present invention is also provide with an apparatus for measuring roundness, which comprises: a table for receiving a work mounted thereon, the work having a circumferential surface with a roundness to be measured; displacement detecting means for detecting displacements on the circumferential surface of the work; rotational driving means for rotationally driving either the table or the displacement detecting means such that the displacement detecting means detects the displacements along the circumferential surface of the work; eccentricity adjusting means for adjusting an eccentricity in the work, the eccentricity adjusting means including means for detecting an adjusted eccentricity by detecting an amount of movement of the table when it is moved in a plane perpendicular to the rotational axis of the rotational driving means; computing means for calculating an eccentricity in the work from the displacements on the circumferential surface of the work detected by the displacement detecting means; and display means for displaying the adjusted eccentricity detected by the means for detecting an adjusted eccentricity and the eccentricity obtained by the computing means as an amount of eccentric compensation.
According to the present invention, an amount of operation given to the eccentricity adjusting means is detected and displayed as an adjusted eccentricity by the means for detecting the adjusted eccentricity. Therefore, the eccentric adjustment can be performed precisely. This eliminates the need for repeating centering operations and can reduce a period of preparation time prior to an actual measurement, improving workability.
The present invention is further provided with an apparatus for measuring roundness, which comprises: a table for receiving a work mounted thereon, the work having a circumferential surface with a roundness to be measured; displacement detecting means for detecting displacements on the circumferential surface of the work; rotational driving means for rotationally driving either the table or the displacement detecting means such that the displacement detecting means detects the displacements along the circumferential surface of the work; tilt adjusting means for adjusting a tilt of the work to the rotational axis, the tilt adjusting means including means for detecting an adjusted tilt by detecting an amount of movement of the table when it is inclined; computing means for calculating the tilt of the work from the displacements on the circumferential surface of the work detected by the displacement detecting means; and display means for displaying the adjusted tilt detected by the means for detecting an adjusted tilt and the tilt obtained by the computing means as an amount of tilt compensation.
According to the present invention, an amount of operation given to the tilt adjusting means is detected and displayed as an adjusted tilt by the means for detecting the adjusted tilt. Therefore, the tilt adjustment can be performed precisely. This eliminates the need for repeating leveling operations and can reduce a period of preparation time prior to an actual measurement, improving workability.
The present invention is still further provided with an apparatus for measuring roundness, which comprises: a table for receiving a work mounted thereon; detecting means for detecting displacements on the work, the work having a circumferential surface with a roundness to be measured; rotational driving means for rotationally driving either the table or the detecting means about a rotational axis; and centering means for obtaining an eccentricity in the work from the rotational axis and compensating the eccentricity on measuring the roundness. In this case, the centering means obtains an angular error between an operational direction of centering and an angular reference of the rotational driving means and centers the work on the basis of the angular error and the eccentricity.
The present invention is still yet further provided with an apparatus for measuring roundness, which comprises: a table for receiving a work mounted thereon; detecting means for detecting displacements on the work, the work having a circumferential surface with a roundness to be measured; rotational driving means for rotationally driving either the table or the detecting means about a rotational axis; and leveling means for obtaining a tilt of the work to the rotational axis and compensating the tilt on measuring the roundness. In this case, the leveling means obtains an angular error between an operational direction of leveling and an angular reference of the rotational driving means and levels the work on the basis of the angular error and the tilt.
The present invention is provided with, in a roundness measurement in which either a work or detecting means is driven rotationally about a rotational axis by rotational driving means to measure a roundness of the work by the detecting means, a method of centering for obtaining an eccentricity in the work from the rotational axis to compensate the eccentricity. The method comprises: obtaining an angular error between an operational direction of centering and an angular reference of the rotational driving means; and centering the work on the basis of the angular error and the eccentricity.
The present invention is also provided with, in a roundness measurement in which either a work or detecting means is driven rotationally about a rotational axis by rotational driving means to measure a roundness of the work by the detecting means, a method of leveling for obtaining a tilt of the work to the rotational axis to compensate the tilt. The method comprises: obtaining an angular error between an operational direction of leveling and an angular reference of the rotational driving means; and leveling the work on the basis of the angular error and the tilt.
As obvious from the forgoing, centering and leveling according to the present invention can be achieved precisely and effectively with a little quantity of operation in consideration of the previously obtained angular error between the angular reference of the rotational driving means and the operational direction of centering or leveling operation.
The angular error may be calculated from central coordinates of the work before and after the work is moved a predetermined amount, for example, in the operational direction of centering. The centering or leveling may be performed in the operational direction of centering or leveling when the angular reference of the rotational driving means is shifted by the angular error. The centering or leveling may also be performed after coordinate transformation of the tilt of the work into a coordinate system relative to the operational direction of centering or leveling based on the angular error.
Other features and advantages of the invention will be apparent from the following description of the preferred embodiments thereof.